the trinity of persons
by the procession of the word and of love in our own mind; and we
have followed him in this (Q. 27, AA. 1, 3). Therefore the trinity of
persons can be known by natural reason.

Obj. 3: Further, it seems to be superfluous to teach what cannot be
known by natural reason. But it ought not to be said that the divine
tradition of the Trinity is superfluous. Therefore the trinity of
persons can be known by natural reason.

_On the contrary,_ Hilary says (De Trin. i), "Let no man think to
reach the sacred mystery of generation by his own mind." And Ambrose
says (De Fide ii, 5), "It is impossible to know the secret of
generation. The mind fails, the voice is silent." But the trinity of
the divine persons is distinguished by origin of generation and
procession (Q. 30, A. 2). Since, therefore, man cannot know, and with
his understanding grasp that for which no necessary reason can be
given, it follows that the trinity of persons cannot be known by
reason.

_I answer that,_ It is impossible to attain to the knowledge of the
Trinity by natural reason. For, as above explained (Q. 12, AA. 4,
12), man cannot obtain the knowledge of God by natural reason except
from creatures. Now creatures lead us to the knowledge of God, as
effects do to their cause. Accordingly, by natural reason we can know
of God that only which of necessity belongs to Him as the principle
of things, and we have cited this fundamental principle in treating
of God as above (Q. 12, A. 12). Now, the creative power of God is
common to the whole Trinity; and hence it belongs to the unity of the
essence, and not to the distinction of the persons. Therefore, by
natural reason we can know what belongs to the unity of the essence,
but not what belongs to the distinction of the persons. Whoever,
then, tries to prove the trinity of persons by natural reason,
derogates from faith in two ways. Firstly, as regards the dignity of
faith itself, which consists in its being concerned with invisible
things, that exceed human reason; wherefore the Apostle says that
"faith is of things that appear not" (Heb. 11:1), and the same
Apostle says also, "We speak wisdom among the perfect, but not the
wisdom of this world, nor of the princes of this world; but we speak
the wisdom of God in a mystery which is hidden" (1 Cor. 2:6, 7).
Secondly, as regards the utility of drawing others to the faith. For
when anyone in the endeavor to prove the faith brings forward rea